The present invention relates to electro-mechanical systems for inspecting the inside of pipes for defects and obstructions, and more particularly, to a push-cable for use in such a system that mechanically and electrically connects a video camera head to a push reel and video circuit.
There are many situations in which it is desirable to inspect the inside of a pipe which is already in place, either underground, in a building, or underwater. For example, sewer and drain pipes frequently need to be internally inspected to determine if there are any obstructions or degradations in couplings which prevent free flow of waste material. It is also desirable to internally inspect steam pipes, heat exchanger pipes, water pipes, gas pipes, electrical conduits and fiberoptic conduits. Frequently, pipes which are to be inspected have an internal diameter of six inches or less. It is sometimes necessary to inspect several hundred feet of pipe.
Over the years, video pipe inspection systems have been developed which typically include a camera which is forced down the interior of the pipe so that its internal walls can be inspected on a video display. Conventional video pipe inspection systems include a push-cable which provides an electro-mechanical connection between a rugged head enclosing the video camera and a rotatable push reel which is used to pay out the cable and force the head down the pipe. Typically, the push-cable incorporates a conventional co-axial cable. Both the relatively stiff mechanical portion of the cable and the electrical portion thereof are arranged in a concentric bundle. Problems arise because the push-cable must be sufficiently stiff in order that the head containing the video camera can be pushed hundreds of feet down the inside of a pipe. However, the cable must also be able to bend sharply so that the video camera head can be forced through a number of tight turns which may include relatively sharp angles, such as ninety degrees.
Heretofore, conventional push-cables which have been constructed for video pipe inspection systems have utilized a miniature seventy-five ohm impedance coaxial cable to carry the video signal. This miniature co-axial cable is relatively expensive and is delicate. Its center conductor wire is relatively small and breaks easily, especially at the end terminations. Another significant disadvantage of the miniature seventy-five ohm coaxial cable is that it tends to have high losses and reduced signal strength of the transmitted video data over lengths even as short as one hundred feet. A reduction in video signal strength results in a loss of fine detail or resolution as well as image contrast in the displayed video. The high frequency part of the video image is attenuated more severely than the lower frequency part of the signal.
Besides improving its signal-to-noise ratio and bandwidth, it would also be desirable to reduce the diameter of a push-cable utilized for video pipe inspection. In general a smaller, lighter push-cable can be pushed further into a pipe.